The present invention relates to a method for setting the instant of opening of a fuel injector in a cylinder of a direct-injection internal combustion engine.
In an engine of this type, particularly one using the xe2x80x9cstratified chargexe2x80x9d mode of combustion, it is important for the fuel involved in the composition of the air/fuel mixture to be burned in the engine cylinders, to be introduced into each cylinder at a moment chosen so that this mixture precisely reaches the electrodes of a spark plug for igniting the mixture at the moment when the electrodes emit a spark. It is only by doing this that correct combustion of the mixture can be ensured and, in particular, that effective protection can be had against any possibility of a misfire.
Significant effort needs therefore to be put into setting the instant of opening of the injector before such an engine can enter service, namely before a motor vehicle powered by this engine can be put in circulation for example.
This setting is made necessary by inevitable manufacturing tolerances affecting various parts of the engine or associated with the latter. Furthermore, during the life of the engine, the instant-of-opening-setting may drift, or need tweaking as a result, for example, of the aging of the aforesaid parts.
These difficulties can be overcome by lengthening the time for which a spark is likely to initiate combustion of the mixture or by multiplying the ignition sparks in such a way that at least one of them is present at the moment when the mixture to be burnt reaches the electrodes of the spark plug.
These measures unfortunately have the effect of shortening the working life of the spark plug, leading to costly replacements thereof.
Furthermore, as the actual instant of ignition of the mixture then remains unknown, the engine management computer conventionally used is unable to evaluate precisely the torque delivered by this engine. Engine control strategies based on knowledge of this torque (elimination of torque surges, rapid reduction of torque when the transmission changes gear, for example) are then difficult, if not impossible, to implement.
It is precisely an object of the present invention to provide a method for setting the instant of opening of a fuel injector in a cylinder of a direct-injection internal combustion engine, that does not suffer from the drawbacks mentioned hereinabove and that, in particular, allows the life of the engine spark plugs to be lengthened, and makes it possible to maximize and estimate precisely the torque delivered by this engine, while at the same time allowing the engine to be adapted easily to produce these results.
This object of the invention, together with others that will become apparent from reading the description that will follow, is achieved using a method for setting the instant of opening of a fuel injector in at least one of the cylinders of a direct-injection internal combustion engine, notable in that: a) a series of sparks is emitted into said cylinder, filled with an air/fuel mixture to be ignited, at predetermined successive instants, b) the one of said sparks that initiates said ignition of said mixture is identified, c) the difference separating the instant of emission of said spark from a predetermined ignition instant able to ensure that said engine supplies a predetermined mechanical power is evaluated, and d) the instant of opening of said fuel injector is corrected as a function of said difference, so as to initiate subsequent ignitions of the air/fuel mixture in said cylinder at said predetermined instant.
As will be seen in detail later on, by virtue of this correction it is then possible, using a single spark, to trigger combustion of the air/fuel mixture in the cylinder in such a way that it extends over a time interval chosen so that the engine then produces a predetermined performance, in terms of delivered torque for example. It is thus possible to set the instant of opening of the injector so that the delivered torque is a maximum, for example, for a given engine speed and load.
The invention also provides a device for implementing this method, comprising a) means able to emit a series of sparks into the engine cylinder when this cylinder is full of an air/fuel mixture that is to be ignited, b) means for detecting ignition of said mixture and delivering a corresponding signal, and c) calculation means sensitive to said signal and able to control, on the one hand, said means for emitting said series of sparks so that said sparks are emitted at predetermined respective instants and, on the other hand, the instant of opening of said fuel injector in said engine cylinder, on the basis of information contained in said signal.